The Moon is not self-luminous, but rather reflects the light
of the distant Sun.

The Moon circles the Earth once per month.

You can demonstrate how the observed phenomena are a consequence of these
assumptions by holding a ball at arm's length in a room illuminated
by a single lamp in the corner. Watch the changing illumination of
the ball as you gradually spin in place one full circle. The phase of the
Moon (the ball) depends on where it is in its orbit with respect
to the Sun (the lamp).

Similarly the day/night cycle may be explained by the following
assumptions:

The Earth is spherical in shape.

The Earth is illuminated by the distant Sun.

The Earth rotates on its axis once each day.

The time of day depends on how much the observer has
rotated with respect to the Sun.

Now both the daily and monthly motions occur simultaneously. So for
example, if we want to know in which direction to look for the Moon, we
need to know both the time of day and the time of the month (the lunar
phase). Answering questions that combine these two motions can be a
bit confusing at first. The purpose of this web site is to introduce
you to a lunar phases diagram which you can use to solve these kinds of
problems.

The layout of the site is straightforward. First, there are three
tutorial pages that explain the elements of the lunar phases diagram
one-by-one. Second, there is the lunar phases tool and quiz. The tool
is an interactive version of the diagram and can be used to solve the
problems posed by the quiz. Once you can answer three questions
correctly in a row, you have mastered the topic! Finally, for the
curious student who wonders whether we have cut some corners in our
basic explanation, there is a page with all the caveats and details we
did not mention earlier.